The invention arose from efforts to develop a microlithography system for processing semiconductor wafers subject to a submicron design rule, though the invention is applicable to a wide variety of uses where seismic isolation is essential, especially those requiring accuracy on an extremely small scale. The invention particularly arose from further development efforts regarding the system in co-pending application Ser. No. 06/735,319, now abandoned filed May 17, 1985.
In microlithography systems for micron and multi-micron design rule capability, the worktable of the system is isolated from floor motion to afford the required accuracy. To accomplish this isolation, systems typically employ a large inertial mass such as a granite block supported above the floor by soft springs such as air bags or air pistons that utilize the compressibility of a gas within a reservoir as the spring mechanism. Lateral isolation is accomplished by designing these vertical soft springs to have as little lateral compliance as possible.
Further miniaturization now requires microlithography systems having submicron design rule capability, such as 0.1 micron overlay accuracy and 0.5 micron resolution. The above noted traditional type isolation techniques are inadequate for the level of accuracy required in submicron systems.
Rather than passive isolation, the noted co-pending application instead or additionally provides inertially augmented active isolation. Furthermore, rather than position stabilization, the noted co-pending application provides force or acceleration counteraction regardless of relative floor position or motion, and variable changing thereof. These features are particularly provided in the present invention by movement of a reaction mass.
The noted co-pending application and the present invention are particularly advantageous in a step and repeat microlithography system where stage motion for each exposure causes a reaction force in its supporting worktable and in turn a vibrational quiver. The noted co-pending application and the present invention significantly reduce the resonant frequency and amplitude of worktable quiver, which in turn significantly reduces the delay time between exposures, and hence increases throughput.